Eagor's Forums » CEN6520 - Project 2 » Router to router offsets?

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Topic: Router to router offsets?

Steven Eagen Posts: 14

Date Posted: 2005-01-30 22:52 David Mauk asked: Router to router offsets? Are the offsets starting from 00000000 through 'big number'(65000 i.e. 11111111) for each segment (fragment group)? IF not where are we getting the offset from? Or maybe it does not matter each person can do what they want (that will probably work too as long as we all increment our offsets based on the current offset of the fragment).

jesse_sweetland Posts: 14

Date Posted: 2005-01-31 07:06 The offset is the byte position within the original segment. Suppose you start with a segment of 500B and the MTU between the first two routers is 100B. You would then have to fragment into 6 fragments: 100B, 100B, 100B, 100B, 100B, and 84B. The first 5 fragments would be 86B data + 14B header, and the last one would be 70B data and 14B header. The respective offsets for each of the fragments would be: 0, 86, 172, 258, 344, and 430. Suppose the MTU on the next hop is 50B. Then you would end up with these fragments: 50B, 50B, 28B, 50B, 50B, 28B, 50B, 50B, 28B, 50B, 50B, 28B, 50B, 50B, 28B, 50B, and 48B. The offsets would then be (respectively): 0, 36, 72, 86, 222, 258, etc.

David Mauk Posts: 17

Date Posted: 2005-02-03 00:34 Good that is as expected.